When Emily was new to Sodor, she was ignored by the other engines for borrowing and pulling Annie and Clarabel without Thomas' permission or knowledge. The matter was resolved after she saved both Thomas and Oliver from a nasty accident on the cross-points and she was rewarded with two new coaches. Emily proved to be kind-hearted, as she was the only engine concerned about Henry when he was ill due to leaky tubes and when she stuck up for Salty when Thomas and Percy were teasing him.
In the seventh season, Emily acts as a sisterly figure to the others. Emily is kind and friendly and always sensitive to the other engines' feelings. If she wrongs someone, knowingly or not, she is quick to apologize.
Emily is based on a Great Northern Railway G3 Stirling Single 4-2-2. Designed by Patrick Stirling in 1870 with 8ft 1in driving wheels and outside cylinders, they were specifically built for high speed expresses between London and York. These locomotives were capable of hauling 280 ton trains at 50 mph, though they could reach 85 mph on lighter services. A total of 53 were built at Doncaster between 1870 and 1895, in three series introduced in 1870, 1884 and 1894 respectively; the last was withdrawn in 1916. The only surviving member of her class (No. 1) is on display at the National Railway Museum.
Emily is painted emerald green with gold and yellow lining. She has chocolate coloured running-boards and her buffers were originally bronze but are now silver.
- Although the second female steam engine to ever appear in the television series (the first being Lady), Emily is the first female steam engine to appear and remain on a regular basis.
- Michael Angelis give Emily a Scottish accent reflecting the origin of her designer.
- According to Emily's Slide Show, she was built around the same time as Donald and Douglas.
- Emily's seventh season whistle sound would later be re-used for Peter Sam.
- Her whistle was also used in the Mr. Men Show episode "Parks".
- According to Robert Gauld-Galliers's concept art, Emily was originally going to have handrails on top of her smokebox, three front coupling chains and a gold builder's plate on her wheel arch.
- Emily was called Emilie in the French dub of the seventh season.